1. Field of the Invention
The present invention relates to a quantum computer and quantum computation method utilizing coupling of an optical cavity with an atom.
2. Description of the Related Art
L.-M. Duan et al. have proposed a new method for realizing a controlled phase flip gate (see, for example, L.-M. Duan and H. J. Kimble, Phys. Rev. Lett. 92, 127902 (2004)). In this proposal, quantum bits are expressed by polarization of photons. However, in quantum computers, it is preferable to express quantum bits using atomic states that are more stable and easily usable as memories.
In light of this, Y.-F. Xiao et al. have proposed a controlled phase flip gate in which a change in light beam intensity in a cavity due to strong coupling between the cavity and an atom is utilized like the method of Duan, but the quantum bits are expressed by ground states of the atoms (see, for example, Y.-F. Xiao, X.-M. Lin., J. Gao, Y. Yang, Z.-F. Han, and C.-C. Guo, Phys. Rev. A 70, 042314 (2004); and Y.-F. Xiao, Z.-F. Han, Y. Yang, and C.-C. Guo, Phys. Lett. A 330, 137 (2004)).
Xiao et al. state in these papers that the methods are scalable since they exhibit a low error rate.
However, Xiao et al. suggest nothing about the specific structure of a quantum computer containing three or more quantum bits. Moreover, even if a researcher in this technical field has mastered the methods proposed by Xiao et al., it is still not obvious for them to contrive any specific structure of the quantum computer containing three or more quantum bits.